Commercialization of ocean wave energy converters or WECs lags significantly behind solar and wind energy even though ocean wave energy is significantly more concentrated, predictable and persistent than the solar energy which produces winds or wind energy that produces ocean waves and swells. Water's relatively high density (over 800 times greater than air) largely accounts for the higher energy density of waves, but also increases the challenges of severe sea-state survivability for WECs. Over 100 WEC designs have been proposed over the last century, yet only a handful of prototypes have been deployed only recently in ocean environments at “commercial scale” (over 150 kw electrical output). No utility scale (over 1 MW) WECs have yet been ocean deployed.
To make such WECs survivable in typical 15 meter severe storm waves, most currently proposed WECs are made of heavy steel plate (like ocean going ships that can survive 15 meter waves). This makes the WECs both expensive and unresponsive (inefficient) during more normal sea-states. Most WECs have buoy like shapes and are known as “point absorbers” and have at least one floating component which moves in response to oncoming waves (i.e., a flop-gate, buoy, float, or raft) flexibly attached to a second moving or relatively stationary component (a seabed, seawall attachment, or a comparable or more massive floating component). As oncoming waves move one component relative to another, a resistive force mechanism absorbs energy (resistive force×distance=energy or work captured).
The “IDEAL WEC” would be light weight (for high wave responsiveness in all sea conditions), low cost, with high energy capture efficiency in most sea-states, and yet be survivable in severe sea states. It would be deployable on the ocean surface and in deep water where wave energy levels are highest and potential conflicts with fishing, boating and shoreline visual impacts are minimized. It would be elongated (in the direction parallel to oncoming wave fronts), rather than circular or buoy like in section, thus intercepting maximum wave front energy per unit of WEC volume and weight and, therefore, have the lowest possible cost per unit of WEC width. Circular section and other narrow-width buoys must square their sectional area and cube their volume (exponentially increasing their weight and cost) to intercept and access the energy from additional oncoming wave fronts. Because exactly half of all deep water wave energy is “potential” or “heave” energy (mass of water between the vertical distance between each crest and trough) with the remaining half “kinetic” energy (from the mass of water particle movement), an efficient WEC must capture most of both wave energy components (or be very inexpensive).
Vertically-heaving buoys can only capture the heave or potential energy component that likely cannot exceed 50% of total wave energy. Near shore deployed floating, bottom pivoting “flap” or “pivoting” or “hinged” gate-type WECs likely can only capture the kinetic or “surge” energy component of near shore waves that have already lost, to bottom friction, a major portion of the energy they contained in deep water.
Another necessity to high wave energy capture efficiency is to match the wave resistive force of the WEC to oncoming waves. If the device is too “stiff” or resistive, it will reflect much or most of the impacting wave, partially or totally canceling succeeding oncoming waves, rather than absorbing the wave's energy. If the device's resistive force is too weak, the wave will pass over, under, or through the WEC rather than being absorbed by it. Because few successive ocean waves are alike, an ideal efficient WEC must sense each successive wave's potential energy and vary the device's resistive force with each wave (or at least adjust to the average wave amplitude and frequency for that time period). If the motion of the WEC itself produces its own waves, those waves carry away energy not absorbed by the WEC, and potentially cancel or reduce the energy of oncoming waves.
WECs which have their mass and buoyancy “tuned” to a specific amplitude and period for optimum performance, (“resonance” dependent WECs) such as with the uniform waves produced in a wave test tank, have dismal performance in real ocean wave conditions that involve random wave amplitudes and periods. The present disclosure provides utility scalable, surface deep-water deployable WEC's with the properties previously described for an “Ideal WEC” including high wave-energy-capture efficiency in real random seas, light weight, low cost, and severe-sea survivability.